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remove polonius fact generation from NLL constraint generation
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@lqd
lqd committed Nov 26, 2023
1 parent c976bc1 commit 626289a
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Showing 2 changed files with 21 additions and 202 deletions.
214 changes: 20 additions & 194 deletions compiler/rustc_borrowck/src/constraint_generation.rs
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Original file line number Diff line number Diff line change
@@ -1,69 +1,45 @@
#![deny(rustc::untranslatable_diagnostic)]
#![deny(rustc::diagnostic_outside_of_impl)]
use rustc_infer::infer::InferCtxt;
use rustc_middle::mir::visit::TyContext;
use rustc_middle::mir::visit::Visitor;
use rustc_middle::mir::{
Body, Local, Location, Place, PlaceRef, ProjectionElem, Rvalue, SourceInfo, Statement,
StatementKind, Terminator, TerminatorKind, UserTypeProjection,
};
use rustc_middle::mir::visit::{TyContext, Visitor};
use rustc_middle::mir::{Body, Location, SourceInfo};
use rustc_middle::ty::visit::TypeVisitable;
use rustc_middle::ty::GenericArgsRef;
use rustc_middle::ty::{self, Ty, TyCtxt};
use rustc_middle::ty::{GenericArgsRef, Region, Ty, TyCtxt};

use crate::{
borrow_set::BorrowSet, facts::AllFacts, location::LocationTable, places_conflict,
region_infer::values::LivenessValues,
};
use crate::region_infer::values::LivenessValues;

pub(super) fn generate_constraints<'tcx>(
infcx: &InferCtxt<'tcx>,
tcx: TyCtxt<'tcx>,
liveness_constraints: &mut LivenessValues,
all_facts: &mut Option<AllFacts>,
location_table: &LocationTable,
body: &Body<'tcx>,
borrow_set: &BorrowSet<'tcx>,
) {
let mut cg = ConstraintGeneration {
borrow_set,
infcx,
liveness_constraints,
location_table,
all_facts,
body,
};

let mut cg = ConstraintGeneration { tcx, liveness_constraints };
for (bb, data) in body.basic_blocks.iter_enumerated() {
cg.visit_basic_block_data(bb, data);
}
}

/// 'cg = the duration of the constraint generation process itself.
struct ConstraintGeneration<'cg, 'tcx> {
infcx: &'cg InferCtxt<'tcx>,
all_facts: &'cg mut Option<AllFacts>,
location_table: &'cg LocationTable,
tcx: TyCtxt<'tcx>,
liveness_constraints: &'cg mut LivenessValues,
borrow_set: &'cg BorrowSet<'tcx>,
body: &'cg Body<'tcx>,
}

impl<'cg, 'tcx> Visitor<'tcx> for ConstraintGeneration<'cg, 'tcx> {
/// We sometimes have `args` within an rvalue, or within a
/// call. Make them live at the location where they appear.
fn visit_args(&mut self, args: &GenericArgsRef<'tcx>, location: Location) {
self.add_regular_live_constraint(*args, location);
self.record_regions_live_at(*args, location);
self.super_args(args);
}

/// We sometimes have `region` within an rvalue, or within a
/// We sometimes have `region`s within an rvalue, or within a
/// call. Make them live at the location where they appear.
fn visit_region(&mut self, region: ty::Region<'tcx>, location: Location) {
self.add_regular_live_constraint(region, location);
fn visit_region(&mut self, region: Region<'tcx>, location: Location) {
self.record_regions_live_at(region, location);
self.super_region(region);
}

/// We sometimes have `ty` within an rvalue, or within a
/// We sometimes have `ty`s within an rvalue, or within a
/// call. Make them live at the location where they appear.
fn visit_ty(&mut self, ty: Ty<'tcx>, ty_context: TyContext) {
match ty_context {
Expand All @@ -74,175 +50,25 @@ impl<'cg, 'tcx> Visitor<'tcx> for ConstraintGeneration<'cg, 'tcx> {
span_bug!(span, "should not be visiting outside of the CFG: {:?}", ty_context);
}
TyContext::Location(location) => {
self.add_regular_live_constraint(ty, location);
self.record_regions_live_at(ty, location);
}
}

self.super_ty(ty);
}

fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
if let Some(all_facts) = self.all_facts {
let _prof_timer = self.infcx.tcx.prof.generic_activity("polonius_fact_generation");
all_facts.cfg_edge.push((
self.location_table.start_index(location),
self.location_table.mid_index(location),
));

all_facts.cfg_edge.push((
self.location_table.mid_index(location),
self.location_table.start_index(location.successor_within_block()),
));

// If there are borrows on this now dead local, we need to record them as `killed`.
if let StatementKind::StorageDead(local) = statement.kind {
record_killed_borrows_for_local(
all_facts,
self.borrow_set,
self.location_table,
local,
location,
);
}
}

self.super_statement(statement, location);
}

fn visit_assign(&mut self, place: &Place<'tcx>, rvalue: &Rvalue<'tcx>, location: Location) {
// When we see `X = ...`, then kill borrows of
// `(*X).foo` and so forth.
self.record_killed_borrows_for_place(*place, location);

self.super_assign(place, rvalue, location);
}

fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
if let Some(all_facts) = self.all_facts {
let _prof_timer = self.infcx.tcx.prof.generic_activity("polonius_fact_generation");
all_facts.cfg_edge.push((
self.location_table.start_index(location),
self.location_table.mid_index(location),
));

let successor_blocks = terminator.successors();
all_facts.cfg_edge.reserve(successor_blocks.size_hint().0);
for successor_block in successor_blocks {
all_facts.cfg_edge.push((
self.location_table.mid_index(location),
self.location_table.start_index(successor_block.start_location()),
));
}
}

// A `Call` terminator's return value can be a local which has borrows,
// so we need to record those as `killed` as well.
if let TerminatorKind::Call { destination, .. } = terminator.kind {
self.record_killed_borrows_for_place(destination, location);
}

self.super_terminator(terminator, location);
}

fn visit_ascribe_user_ty(
&mut self,
_place: &Place<'tcx>,
_variance: ty::Variance,
_user_ty: &UserTypeProjection,
_location: Location,
) {
}
}

impl<'cx, 'tcx> ConstraintGeneration<'cx, 'tcx> {
/// Some variable with type `live_ty` is "regular live" at
/// `location` -- i.e., it may be used later. This means that all
/// regions appearing in the type `live_ty` must be live at
/// `location`.
fn add_regular_live_constraint<T>(&mut self, live_ty: T, location: Location)
/// Some variable is "regular live" at `location` -- i.e., it may be used later. This means that
/// all regions appearing in the type of `value` must be live at `location`.
fn record_regions_live_at<T>(&mut self, value: T, location: Location)
where
T: TypeVisitable<TyCtxt<'tcx>>,
{
debug!("add_regular_live_constraint(live_ty={:?}, location={:?})", live_ty, location);

self.infcx.tcx.for_each_free_region(&live_ty, |live_region| {
let vid = live_region.as_var();
self.liveness_constraints.add_location(vid, location);
debug!("add_regular_live_constraint(value={:?}, location={:?})", value, location);
self.tcx.for_each_free_region(&value, |live_region| {
let live_region_vid = live_region.as_var();
self.liveness_constraints.add_location(live_region_vid, location);
});
}

/// When recording facts for Polonius, records the borrows on the specified place
/// as `killed`. For example, when assigning to a local, or on a call's return destination.
fn record_killed_borrows_for_place(&mut self, place: Place<'tcx>, location: Location) {
if let Some(all_facts) = self.all_facts {
let _prof_timer = self.infcx.tcx.prof.generic_activity("polonius_fact_generation");

// Depending on the `Place` we're killing:
// - if it's a local, or a single deref of a local,
// we kill all the borrows on the local.
// - if it's a deeper projection, we have to filter which
// of the borrows are killed: the ones whose `borrowed_place`
// conflicts with the `place`.
match place.as_ref() {
PlaceRef { local, projection: &[] }
| PlaceRef { local, projection: &[ProjectionElem::Deref] } => {
debug!(
"Recording `killed` facts for borrows of local={:?} at location={:?}",
local, location
);

record_killed_borrows_for_local(
all_facts,
self.borrow_set,
self.location_table,
local,
location,
);
}

PlaceRef { local, projection: &[.., _] } => {
// Kill conflicting borrows of the innermost local.
debug!(
"Recording `killed` facts for borrows of \
innermost projected local={:?} at location={:?}",
local, location
);

if let Some(borrow_indices) = self.borrow_set.local_map.get(&local) {
for &borrow_index in borrow_indices {
let places_conflict = places_conflict::places_conflict(
self.infcx.tcx,
self.body,
self.borrow_set[borrow_index].borrowed_place,
place,
places_conflict::PlaceConflictBias::NoOverlap,
);

if places_conflict {
let location_index = self.location_table.mid_index(location);
all_facts.loan_killed_at.push((borrow_index, location_index));
}
}
}
}
}
}
}
}

/// When recording facts for Polonius, records the borrows on the specified local as `killed`.
fn record_killed_borrows_for_local(
all_facts: &mut AllFacts,
borrow_set: &BorrowSet<'_>,
location_table: &LocationTable,
local: Local,
location: Location,
) {
if let Some(borrow_indices) = borrow_set.local_map.get(&local) {
all_facts.loan_killed_at.reserve(borrow_indices.len());
for &borrow_index in borrow_indices {
let location_index = location_table.mid_index(location);
all_facts.loan_killed_at.push((borrow_index, location_index));
}
}
}
9 changes: 1 addition & 8 deletions compiler/rustc_borrowck/src/nll.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -149,14 +149,7 @@ pub(crate) fn compute_regions<'cx, 'tcx>(
} = constraints;
let placeholder_indices = Rc::new(placeholder_indices);

constraint_generation::generate_constraints(
infcx,
&mut liveness_constraints,
&mut all_facts,
location_table,
body,
borrow_set,
);
constraint_generation::generate_constraints(infcx.tcx, &mut liveness_constraints, body);
polonius::emit_cfg_and_loan_kills_facts(
infcx.tcx,
&mut all_facts,
Expand Down

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